Theory Ex1

theory Ex1
imports LCF
header {*  Section 10.4 *}

theory Ex1
imports LCF
begin

axiomatization
P :: "'a => tr" and
G :: "'a => 'a" and
H :: "'a => 'a" and
K :: "('a => 'a) => ('a => 'a)"
where
P_strict: "P(UU) = UU" and
K: "K = (%h x. P(x) => x | h(h(G(x))))" and
H: "H = FIX(K)"


declare P_strict [simp] K [simp]

lemma H_unfold: "H = K(H)"
apply (simplesubst H)
apply (rule FIX_eq [symmetric])
done

lemma H_strict [simp]: "H(UU)=UU"
apply (simplesubst H_unfold)
apply simp
done

lemma H_idemp_lemma: "ALL x. H(FIX(K,x)) = FIX(K,x)"
apply (tactic {* induct_tac @{context} "K" 1 *})
apply simp
apply (simp split: COND_cases_iff)
apply (intro strip)
apply (subst H_unfold)
apply simp
done

lemma H_idemp: "ALL x. H(H(x)) = H(x)"
apply (rule H_idemp_lemma [folded H])
done

end